The subject of the present invention is a novel process for isolating milk proteins, the composition, milk protein isolate or milk protein fraction, resulting therefrom and its applications, in particular its food and pharmaceutical applications.
Several prior art documents describing the purification of milk proteins are known.
The document EP-253395 describes the production of a bovine lactoferrin of high purity (>80% in a single step or >98% in two steps) by adsorption of milk or of whey onto a cation-exchange resin comprising carboxymethyl radicals, followed by rinsing and desorption of the lactoferrin.
The document EP-348508 also describes a process for preparing a bovine lactoferrin of high purity (>95%) by adsorption of milk or whey onto a cation-exchange resin of the polysaccharide type comprising sulfuric acid ester functional groups and elution with an aqueous salt solution.
The document EP-298875 describes a process which makes it possible to isolate certain whey proteins by adsorption onto a porous mineral support in the form of grains, these grains being coated with an amine-containing polysaccharide layer having at the surface acid functional groups such as carboxylic or sulfonic groups.
The document EP-418704 describes a process for sequentially purifying lactoferrin and lactoperoxidase by elution on a column loaded with a polysaccharide resin grafted by sulfonic acid groups.
The document U.S. Pat. No. 6,096,870 describes a process for the sequential separation of whey proteins by elution on cationic resins.
The document EP-1017286 describes a process for the sequential separation of whey proteins by radial flow chromatography.
Lactoferrin and lactoperoxidase are milk proteins with advantageous properties, their capacity to bind iron confers on them a role of antibacterial agent against bacteria whose metabolism requires large quantities of iron. Lactoperoxidase is essential for labeling protein with iodine. Lactoferrin promotes the growth of lymphocytes and promotes the absorption of iron by the body; it regulates the differentiation of leukocytes and it inhibits the peroxidation of lipids.
However, all these documents relate to processes aimed at a lactoferrin and/or a lactoperoxidase which are as pure as possible, that is to say processes aimed at reducing as much as possible the proportion of the other proteins initially present in milk or whey. In addition, the conditions for binding the raw material and for eluting the proteins are gentle conditions, with slow flow of materials. On the other hand, the objective which the applicant set itself is the production of a milk protein fraction comprising, among other constituents, lactoferrin and lactoperoxidase, but comprising especially a higher proportion of the other proteins than in the starting milk or whey. For that, the applicant has developed a process with much higher flows than those described in the documents analyzed above, this process allowing a more selective binding in relation to certain proteins.
The document WO93/13676 discloses a process which makes it possible to isolate lactoferrin and lactoperoxidase from whey by passage over a cation-exchange resin at high flow. This process is distinguishable from the process according to the present invention in that the flow is greater than in the process according to the invention (greater than 5 m/h) and in that it aims to purify the lactoferrin and the lactoperoxidase, and not to obtain a particular milk protein fraction containing a relatively high level of the other proteins and endowed with improved biological properties.
There is also known, from the document EP-704218, an agent intended for strengthening the bones, this agent comprising a basic protein fraction or a basic peptide fraction, derived from milk and obtained by passing milk over a cationic resin and eluting. However, the adsorption and elution conditions described in this document are distinct from those used in the process according to the invention and make it possible to isolate a protein fraction distinct from that obtained according to the present invention.
The documents JP-8165249, JP-9187250, JP-9294537 and EP-1010430 describe compositions intended for strengthening the bones and/or for preventing periodontal diseases, these compositions comprising a milk-derived basic protein fraction obtained by adsorption of the milk and elution on a cationic resin. However, the adsorption and elution conditions described in these documents are distinct from those used in the process according to the invention and make it possible to isolate a protein fraction distinct from that obtained according to the present invention.
Thus, it is surprising that the applicant has discovered a novel process for isolating milk proteins which make it possible to obtain a milk protein fraction endowed with improved biological properties, in particular a milk protein fraction promoting growth of the osteoblasts and inhibition of the proliferation of the preosteoclasts and of the osteoclasts.